This application is a complete application filed under 35 U.S.C. xc2xa71.111(a) and claims pursuant to 35 U.S.C. xc2xa7119(a), the date of Korean Patent Nos. 2000-522007 and 2001-35005 filed on Sep. 4, 2000 and Jan. 22, 2001, respectively. The Korean Patent Nos. 2000-52207 and 2001-3585 are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a drying unit for a liquid electrophotographic printing apparatus that is used in printing on printing paper an image developed on a photosensitive medium using a liquid carrier as a mediator. Specifically, the drying unit of the present invention dries the carrier remaining in the photosensitive medium. Additionally, the present invention relates to a liquid carrier drying method using the same, and more particularly, to a drying unit for a liquid electrophotographic printing apparatus having the structure where a liquid carrier on the photosensitive medium can be dried in a non-contacting way.
2. Description of the Related Art
Generally, a liquid electrophotographic printing apparatus forms an electrostatic latent image on a photosensitive medium such as a photosensitive drum or a photosensitive belt and operates as an image forming unit that can obtain a desired image by developing the electrostatic latent image with a toner of certain colors and transferring it onto a printing paper.
With reference to FIG. 1, a general liquid electrophotographic printing apparatus scans laser beams using laser scanning units 21, 23, 25 and 27 and forms an electrostatic latent image on a photosensitive belt 11 circulating along a predetermined path, and develops the electrostatic latent image using developing units 30, 40, 50 and 60. Then, after a drying unit 70 dries the liquid carrier remaining on the photosensitive belt 11, a dried image is transferred from a transfer unit 80 onto a printing paper P, and is thus printed. The photosensitive belt 11 rotates by being wound around a driving roller 13, a transfer backup roller 15 and a steering roller 17.
Each of the developing units 30, 40, 50 and 60 on which a predetermined voltage is applied comprise developing rollers 31, 41, 51 and 61 that are positioned face to face while maintaining a developing gap G when developing the electrostatic latent image; injectors 33, 43, 53 and 63 that provide ink inside the developing gap G; and squeegee rollers 35, 45, 55 and 65 that are positioned on the photosensitive belt 11 in such a way that the belt is pressured. The developing units 30, 40, 50 and 60 make a film of an image developed on the photosensitive belt 11. The ink provided through the injectors 33, 43, 53 and 63 consists of a toner that forms a color image transferred on the printing paper and a liquid carrier that transfers the toner to a region where an electrostatic latent image of the photosensitive belt 11 is formed.
The drying unit 70 absorbs and evaporates the liquid carrier containing the image developed on the photosensitive belt 11, and the liquid carrier is then recycled by condensation and filtration. For this purpose, the drying unit 70 comprises a manifold 71, a drying roller 72, a regeneration roller 73, a heater 74, a ventilation channel 75, a condenser 76, a ventilation pump 77 and a filter 78. Also, the drying unit 70 comprises a pressing device (not shown) such that, according to various modes, i.e., a home mode, a printing mode and a standby mode, the drying roller 72 is selectively in or out of contact with the photosensitive belt at a predetermined pressure and the regeneration roller 73 is selectively in or out of contact with the drying roller 72.
The drying roller 72 is equipped in the manifold 71 and installed such that the drying roller can be in contact with the face where the image of the photosensitive belt 11 is formed by the pressing device. An absorbing layer 72a is equipped outside the perimeter of the drying roller 72 and the carrier remaining on the surface of the photosensitive belt 11 is absorbed through the absorbing layer 72a. 
The regeneration roller 73 is equipped in the manifold 71 in such a way that it can be in contact with the drying roller 72, and inside is equipped with a heater 74 that heats the regeneration roller 73. The carrier absorbed in the absorbing layer 72a of the drying roller 72 is evaporated at the regeneration roller 73 heated by the heater 74. This evaporated carrier is discharged through the ventilation channel 75 connected to the manifold 71 by the pumping action of the ventilation pump 77. The condenser 76 is equipped on the ventilation channel 75 and condenses the carrier moving through the ventilation channel 75. Here, the condensed carrier is separated from the water that is condensed with the carrier and re-supplied to the developing units 30, 40, 50 and 60 through another supply channel (not shown). The carrier that is not condensed is discharged after being filtered by the filter 78.
Meanwhile, a discharging device 91 that irradiates lights and removes charges remaining in the photosensitive belt 11; a charging device 93 that charges up to a predetermined voltage after removing charges; and a plurality of topping chargers 94, 95 and 96 that elevate the surface voltage of the photosensitive belt 11 after developing each color are installed proximate to the photosensitive belt 11 of the liquid electrophotographic printing apparatus.
The transfer unit 80 is positioned, at an interval of the photosensitive belt 11, facing the transfer backup roller 15, and comprises a transfer roller 81 where an image I developed at the photosensitive belt 11 is transcribed and a fuser roller 83 that is positioned at an interval for the printing paper P facing the transfer roller 81, thus immobilizing the printing paper P. Here, the image transcribed on the transfer roller 81 is transcribed on the printing paper P supplied between the transfer roller 81 and the fuser roller 83.
In the prior liquid electrophotographic printing apparatus comprising as described above, the drying unit is structured such that the drying roller contacts with the photosensitive belt and absorbs the liquid carrier. Thus the contacting time at the work point of the photosensitive belt is short and this contacting time is not enough for absorbing the liquid carrier. Therefore the prior printing apparatus has a disadvantage of a low drying efficiency. In particular, since drying is not sufficient enough in continuous printing, it causes a bad transfer of the image on the printing paper. At the same time, due to the bad drying, the liquid carrier is absorbed in the transfer roller, which in turn cause wrinkles in the printing paper, which induces a jam in the printing paper.
Also, since the drying roller contacts with the region where the image on the photosensitive belt is formed, the quality of the image is badly affected by picking the image on the photosensitive belt. In addition, since the picked image remains in the drying roller and the regeneration roller and is transmitted back to the photosensitive belt, it thereby contaminates other images on the photosensitive belt.
Furthermore, since the drying unit is of the contact-type, abrasion and contamination make the drying unit have a limited lifetime after printing several ten thousands times. Therefore, since it should be replaced after this limited lifetime, the maintenance cost is excessively high.
The present invention is contrived after considering the problems described above, and it is an object of the present invention to provide a drying unit for a liquid electrophotographic printing apparatus such that a liquid carrier on a photosensitive belt is dried in a non-contacting way, and a liquid carrier drying method using the drying unit.
To achieve the above objective, a drying unit for a liquid electrophotographic printing apparatus of the present invention comprises a developing unit that develops an image on a photosensitive medium using a liquid carrier as a mediator and a transfer unit that transcribes the developed image on a printing paper, so that the liquid carrier remaining on the photosensitive medium can be dried. The drying unit comprises a manifold having at least one inlet which is positioned near the photosensitive medium and opposite to the photosensitive medium that is open and through which hot air flows in; at least one outlet through which the carrier evaporated from the photosensitive medium by the hot air flowing in is discharged; an inlet-outlet channel connecting the inlet to the outlet; a gas flowing means by which the gas in the manifold is discharged through the outlet and gas flows in the manifold through the inlet; a condenser that is positioned on the inlet-outlet channel and that condenses the evaporated carrier discharged through the outlet; and a heater that is located on the inlet-outlet channel and that heats the gases flowing in the manifold through the inlet.
Also, a drying unit for a liquid electrophotographic printing apparatus is provided that comprises a heating means that is installed in parallel to the running direction of the photosensitive belt, out of contact with the photosensitive belt and that generates heat in order to dry and evaporate the liquid carrier; a manifold that surrounds the heating means and that collects the gas carrier evaporated by the heating means; an inlet-outlet channel that forms the path for circular movement of the gas carrier collected in the manifold by forming a closed loop in communication with the manifold; at least one gas flowing means which is installed on the inlet-outlet channel that circulates the gas carrier along the inlet-outlet channel; an inlet duct which is installed through the manifold and through which the gas carrier evaporated by the heating means flows in communication with the inlet-outlet channel; and a ventilation duct which is installed in communication with the inlet-outlet channel so that air flows in the manifold.
In addition, to achieve the above objective, the invention provides a liquid carrier drying method using a drying unit for the liquid electrophotographic printing apparatus, the drying unit comprising a developing unit that develops an image on a photosensitive medium using a liquid carrier as a mediator and a transfer unit that transcribes the developed image on a printing paper, so that the liquid carrier remaining on the photosensitive medium can be dried. The drying method comprises the steps of calculating the amount of the liquid carrier on the photosensitive medium determining the air injection condition according to the calculated amount of the liquid carrier; heating injection air according to the determined condition and evaporating the carrier on the photosensitive medium by injecting the heated gas at a predetermined speed into the manifold positioned near the photosensitive medium with a surface facing the photosensitive medium and open; discharging out of the manifold the carrier evaporated from the photosensitive medium and the air flowing in through the inlet-outlet channel; condensing the evaporated carrier at the manifold; reheating the gas that remains uncondensed, and injecting the gas at a predetermined speed into the manifold.